A subset of mammalian genes are subject to genomic imprinting, an epigenetic process that results in the differential expression of the two parental alleles of a gene. The maternally expressed H19 gene encodes an untranslated RNA and deletions encompassing the murine H19 locus have demonstrated that H19 sequences regulate imprinting of the cis-linked paternally expressed Igf-2 and Ins -2 genes. Untranslated RNAs are associated with at least three imprinted chromosomal regions, and recent experiments suggest that the H19 RNA may act to regulate imprinting of its own flanking sequences. One goal of this research project is to generate defined changes at the H19/Igf-2 locus using homologous recombination to determine if the H19 RNA is required for it's own imprinting or that of cis-linked genes. A second objective is to use a gene targeting strategy to establish whether H19 can autonomously imprint an unrelated gene in a heterologous chromosomal location. Dysregulation of H19 and Igf-2 imprinting occurs in both Beckwith-Wiedemann Syndrome and Wilm's tumor and several other human disease states are believed to result from mutations disrupting imprinted gene expression. The overall goal of the research described here is to elucidate the molecular mechanisms that control genomic imprinting in mammals using H19 and Igf-2 as a model system.